In general, a light emitting diode (LED) is a device that emits light when electrons and holes meet at a P-N junction by applying a current. The LED has many advantages over conventional light sources, such as continuous light emission at a low voltage and low current and low power consumption.
Particularly, LEDs are widely used for various display devices, backlight sources, and the like. In recent years, technologies for emitting white light by using three light emitting diode chips emitting red, green and blue light respectively or by using a fluorescent substance to convert the wavelength of light have been developed and are expanding in application range even to lighting devices.
An LED that emits ultraviolet light may be used in water purifiers, sterilizers, and the like for the purpose of sterilization, cleaning, and the like, and may also be used in an exposure apparatus that forms a photoresist pattern. Particularly, for a light emitting module including the LED for emitting ultraviolet light used in the exposure apparatus, it is important to concentrate light on a certain target area.
When the LED, which has a relatively small light amount compared to a lamp having a large light amount, is used as a light source to concentrate the power of the light source on an optical fiber or a detector having a size comparable to that of the light source, it is difficult to concentrate the power of the light source over the entire area of the detector using the simple form of a reflector.